Thermal stability and protective properties of phenylphosphonic acid on Cu(111)

Phenylphosphonic acid (PPA) adsorbed on Cu(111) has been studied by synchrotron radiation-based techniques in combination with density functional theory calculations. The dehydrogenated phenylphosphonic acid molecule (PP) strongly bound in a tridentate geometry through oxygen atoms to Cu(111) is shown to be the dominant surface species in the temperature range 150-300 degrees C. The stable PP adlayer substantially protects the Cu(111) surface from oxidation during exposure to ambient conditions. Thermal treatment of the PPA adlayer at 375 degrees C initiates molecular decomposition through several channels: P-O bond scission forming C6H5PO2; C-P bond scission forming phenyl and PO3; and C-H bond scission forming C6H4PO3. All three reaction steps have activation barriers of 1.7-1.8 eV. Small products such as O, H, and phenyl can immediately react further and desorb, while the remaining phosphonate species undergo condensation. After annealing at a higher temperature, the phosphonate group is further reduced from oxygen-rich to phosphorus-rich species, which form the majority of remaining adsorbates after 500 degrees C treatment.

Automated summary

The adsorption of phenylphosphonic acid (PPA) on Cu(111) was studied and it was found that the dehydrogenated phenylphosphonic acid molecule (PP) is the dominant surface species in the temperature range 150-300 degrees C. The stable PP adlayer effectively protects the Cu(111) surface from oxidation. Furthermore, thermal treatment of the PPA adlayer leads to molecular decomposition and subsequent formation of phosphorus-rich species at higher temperatures.